In this model we study the dynamics and control of hepatitis B virus (HBV) infection which is a major health problem worldwide by considering condom, vaccination and treatment as control measures. Initially we determined the basic reproduction number R_0 for the model and observe that once R_0<1, the disease free equilibrium will be stable and HBV infection can be controlled using the three control measures and we also study the solution of the endemic equilibrium point of the model. Next we take the sensitivity analysis of the basic reproduction number of HBV infection and obtain that the endemicity of the infection will reduce with the controls. Finally, the numerical simulation result shows that combination of condom, vaccination and treatment is the most effective way to control hepatitis B infection.

We proposed and solved a combined control malaria system of fifteen ordinary differential equations modeling the transmission dynamics of malaria between humans and mosquitoes. Since our aim is to minimize the number of exposed and infectious human, we discussed the disease free equilibrium and estimated the basic reproduction number using the next generation matrix method. The disease free equilibrium was asymptotically stable when the reproduction number is less than one and unstable when it is greater than one. Numerical results are provided using matlab software to confirm the analyzed results. Our findings were that malaria may be controlled using the combined control method, the insecticide treated bed nets, fumigation of the surroundings and active malaria drug as this will reduce the contact rate between human and mosquito through reduction in mosquito population and malaria transmission.

We investigated the intracellular delay effect on the stability of the endemically infected steady state by analyzing a nonlinear ordinary differential equation model of hepatitis B virus (HBV) infection that considers the interaction betweena replicating virus, hepatocytes and the cytotoxic T lymphocytes (CTL). We gave a criterion to ensure that the infected steady state is asymptotically stable for all delays. A critical delay below which the CTL (immune control mechanism) can be significantly helpful in controlling the HBV infection even when the basic reproduction number is high is allowed in the analysis.

Program files damage and other computer virus symptoms has become a very threatening issue to computer performance. This paper considered an  model with incidence of infected and program files damaged computers and saturated incidence of vaccination and treatment function. Two control functions have been used; one for vaccinating the susceptible computer population and the other for the treatment of the program files damaged computer population. The Pontryagin’s Maximum Principle has been used to characterize the optimal control whose numerical results show the positive impact of the two controls used for controlling the infection dynamics of computer virus. Actually the intention of this study is to minimize the number of infected and program files damaged computer systems and at the same time minimize the cost associated to the controls. Efficiency analysis is also studied to determine the best control strategy among vaccination and treatment. Numerical simulations were carried out in this model to demonstrate the analytical results and it was revealed that combination of vaccination and treatment is the most successful way to minimize the incidence of program files damage.

We designed a simulation of an intracellular differential equation model of the dynamics of malaria with immune control and treatment which considered malaria parasites in the liver and blood. We considered transmission dynamics of malaria and the interaction between the infection in the liver and blood. The disease free equilibrium of our model was asymptotically stable when the basic reproduction number is less than one and unstable when it is greater than one. Numerical simulations show that if the immune response is strong with effective treatment, malaria infection will be cleared from an infectious human host. A treatment strategy using highly effective drugs against malaria parasites with strong immune response can reduce malaria progression and control the disease.